John KD5YI wrote:
Wake up, Cecil. The 6.75 inch long Texas Bugcatcher coil falls into the
lumped component category (being only .002WL at 75m).

Sorry John, we are not talking about *physical* length
- we are talking about *electrical* length which, like
a piece of coax, depends upon the velocity factor. The
velocity factor for a Texas Bugcatcher coil is ~0.02.

6.75"/0.02=337.5", 337.5"/12 = 28 feet,
28'/(246'/lamda) = 0.114 WL

Thus a 75m Texas Bugcatcher loading coil is electrically
about 41 degrees long at 4 MHz. Hint: It is a slow-wave
structure described in "Fields and Waves ..." by
Ramo, Whinnery, and Van Duzer, 3rd edition, page 476.

The equation for the approximate velocity factor for
an RF coil meeting the specified physical conditions
is given in equation 32 on page 4 of:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

Fig. 1 gives the VF for various diameter/wavelength
ratios and turns/wavelength. Here's how to determine
the VF from the Fig. 1 graph.

For the coil in question, calculate the
diameter/wavelength ratio and plot it on the x axis.

The diameter/wavelength ratio for the Texas Bugcatcher
is ~0.5/246 = 0.002, i.e. 2x10^-3 on the graph.

For the coil in question, calculate the
turns/wavelength ratio and select the proper curve.

The turns/wavelength ratio for the Texas Bugcatcher
is 4tpi*12*246' = 11,800, i.e. slightly to the left
of the left-most 10k curve.

That puts the Texas Bugcatcher squarely in the slow-
wave category with a velocity factor of ~0.02.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com